JP2000-173630A discloses a method of manufacturing a fuel cell separator. According to the manufacturing method, a kneaded mixture is prepared by mixing 80-95% by weight of scaly natural graphite powders or expanded graphite powders with 5-20% by weight of thermosetting resin containing not less than 65% nonvolatile matter. The kneaded mixture is granulated, and granulated pellets of 10-1000 μm diameters are filled in a molding container. The fillings in the molding container are then isotropically pressure-molded to a molded product of predetermined shape, and are thermally cured by a temperature ranging between 150° C. and 280° C.
JP2003-109622A discloses another method of manufacturing a fuel cell separator. According to this manufacturing method, a mixture composition, containing thermo plastic resin and graphite particles, is formed. The mixture composition is filled in a heated state into a cavity of a die, which has been preheated to a temperature not lower than a melting point of the thermoplastic resin. The mixture composition is melted and compressed uniformly at a predetermined pressure for forming. The mixture composition is then cooled to a temperature lower than a heat deflection temperature of the thermoplastic resin while the pressure is being applied to the die.
JP1999 (11)-354138A discloses a method of forming a ribbed separator for a fuel cell. According to the forming method, a mixture of expanded graphite granulated powders and thermosetting or thermoplastic resin is employed as a material. The mixture is hot-press molded by a die to a ribbed separator for a fuel cell.
JP1998 (10)-3931A discloses a method of forming a separator, according to which a primary material mixed with carbonic material and hydrophilic material is filled in a metal die and press molded to a separator.
The above-described fuel cell separator is required comprehensively to exhibit excellent gas shielding; excellent creep resistance; and low electric resistance (excellent electric conductivity). Especially, where an expanded graphite material, which has a low bulk density, is used, even if the expanded graphite material is pressure-molded, there may be limitations to improve gas shielding of the separator. Especially, a separator portion, which serves as an outer edge portion and has a thick plate thickness, exhibits a less compression amount than a separator portion having a thin plate thickness, at which passages are formed on a surface. Therefore, the separator portion having the thick plate thickness may not be able to be densified to a sufficient level, so that there may be limitations to improve gas shielding of the outer edge portion of the separator.
Furthermore, according to the above-described fuel cell separator, as illustrated in FIG. 18, a flat sheet 300 having two surfaces 301 and 302 oppositely arranged to each other is prepared for the purpose of manufacturing a separator 350. More specifically, the flat sheet 300 is compressed in a thickness direction by means of a pressurizing die, in such a manner that the sheet 300 is pressure molded to form recessed groove-like shaped surface passages 305, which direct flows of reactant gas. According to this method of manufacturing the separator 350, although the surface passages 305 can be formed on the sheet 300, outer edge portions 352 of the separator 350 exhibits a less compression amount than a separator portion 354 on which the surface passages 305 are formed. Therefore, the outer edge portions 352 are not densified to a sufficient level, therefore gas shielding of the outer edge portions 352 are less effective.
Therefore, if the outer edge portions 352 are loaded with a larger pressurizing force simply to exert a larger compression amount and to enhance their gas shielding, the compression amount of the separator portion 354, on which the surface passages 305 are formed, are further increased, which may cause cracks on the separator portion 354. In this case, a molding load applied to the sheet 300 may become excessively large. As described above, the conventional methods of manufacturing the fuel cell separator may not be considered to comprehensively satisfy characteristics required to the fuel cell separator, such as excellent gas shielding, high creep resistance, low electric resistance, and so on.
The present invention has been made in view of the above circumstances, and provides a method of manufacturing a fuel cell separator, by which the fuel cell separator comprehensively excels in assuring, therein, gas shielding, creep resistance and electric conductivity, and also provides the fuel cell separator.